A well is typically completed by installing a casing string into a wellbore. Production equipment can then be installed into the well to enable production of hydrocarbons from one or more production zones in the well. In performing downhole operations, communications between a downhole component and surface equipment is often performed.
A common type of communications link includes a wireline in which one or more electrical conductors route power and data between a downhole component and the surface equipment. Other conveyance structures can also carry electrical conductors to enable power and data communications between a downhole component and surface equipment. To communicate over an electrical conductor, a downhole component typically includes electrical circuitry and sometimes power sources such as batteries. Such electrical circuitry and power sources are prone to failure for extended periods of time in the typically harsh environment (high temperature and pressure) that is present in a wellbore.
Another issue associated with running electrical conductors in a wireline, or other type of conveyance structure, is that in many cases the wireline extends a relatively long length (thousands to tens of thousands of feet). The resistance present in such a long electrical conductor is quite high, which results in high electrical power dissipation in the long conductor. As a result, surface units of relatively high power are typically used in a well application to enable communications along the electrical conductors.
To address some of the issues associated with use of electrical conductors to communicate in a wellbore, optical fibers are used. Communication over an optical fiber is accomplished by using an optical transmitter to generate and transmit laser light pulses that are communicated through the optical fiber. Downhole components can be coupled to the optical fiber to enable communication between the downhole components and surface equipment. Examples of such downhole components include sensors, gauges, or other measurement devices.
Typically, an optical fiber is deployed by inserting the optical fiber into a control line, such as a steel control line, that is run along the length of other tubing (e.g., production tubing). The control line is provided as part of a production string that is extended into the wellbore. Although extending optical fibers through a control line have been proved to be quite useful in many applications, such control lines are generally not useful in other applications. For example, in some cases, it may be desired to run an intervention, remedial, or investigative tool into a wellbore. Conventionally, such intervention, remedial, or investigative tools are carried by a wireline, slickline, coiled tubing, or some other type of conveyance structure. If communication is desired between the intervention, remedial, or investigative tool and the surface equipment, electrical conductors are run through the conveyance structure. As noted above, electrical conductors are associated with various issues that may prove impractical in some applications.